I was trying to an export of a mailbox using the New-MailboxExportRequest CMDlet in Exchange 2010 SP1. However instead of creating a PST it gave me an error.

Unable to open PST file ‘\\Server\Exports\Test.pst’. Error details: Access to the path ‘\\ExServer1\Imports\Test1.pst’ is denied.;

Microsoft.Exchange.MailboxReplicationService.RemotePermanentException: Access to the path ‘\\Server\Exports\Test.pst’ is denied.

I was soon pointed into the right direction by a blog post by Tony Redmond. He indicated that because the Mailbox Replication Server (MRS) is running as LocalSystem it can’t access a network share. By adding the Exchange Trusted Subsystem group to the share permissions you will give the LocalSystem account and therefore MRS access to the share.